The present invention relates to an information retrieval apparatus and a method to present high quality information to a user quickly in a network system.
Recently, the World Wide Web (xe2x80x9cWWWxe2x80x9d) is widely used. In the Internet or Intranet, electric information is easily accessable. Therefore, a so-called information flood occurs and the user can not easily extract his desired data from vast information. In order to reduce this problem, retrieval systems (i.e., search engines) appeared in the Internet or Intranet. As a retrieval system, xe2x80x9cAltavistaxe2x80x9d of DEC and xe2x80x9cexcitexe2x80x9d of Excite corporation are well known. When a retrieval request is received from the user as a retrieval expression, the retrieval system presents the information (Web pages) which best related with the retrieval expression. In this case, a web page as a retrieval object is preserved as a format of an index table and quickly retrieved. However, if a large number of retrieval requests are received at once from many users in the world, it takes a long time to process all of them.
Accordingly, in order to quickly respond to the user for at least one retrieval request, the system caches the previous retrieval result. In this technique, if the information is retrieved from the database by the retrieval expression, the information is stored in a storage device (cache memory) as the retrieval result. Hereafter, when the retrieval request is the same as before, at least one retrieval result is extracted from the storage device and quickly presented to the user. In short, after the second retrieval request, the database is not actually retrieved and the information is provided to the user by referring to the cache content. This technique is disclosed in Japanese Patent Disclosure (Kokai) H4-199468, H4-326163.
However, in this kind of the retrieval system, the quality of the retrieval result is not taken into consideration because a fast retrieval and a high quality of the retrieval result conflict with each other. In short, when an accurate retrieval algorithm improves the quality of the retrieval result, but it takes a long time. On the other hand, in case of the retrieval is executed by a profile (interest topic) by unit of the user, the retrieval results stored in the cache memory is not effective for other users. In the latter case, the response time to present the retrieval result to the user is long because the information is normally retrieved from the database.
Now, characteristics of WWW retrieval in their present condition will be analysed.
Firstly, a huge number of requests come randomly. A large number of the retrieval requests are received through a network, but it is necessary to quickly respond to these retrieval request. Each user respectively locates a terminal connected to the network. Therefore, each retrieval request reaches the retrieval system at random.
Secondly, same retrieval expressions are requested often. A large number of retrieval requests are not different each other. About seventy percent of the retrieval expressions are same. Especially, in the WWW, many users want to know new information. In general, the kind of the new information is limited and the retrieval requests often are the same retrieval expression.
Thirdly, the retrieval with a sophisticated algorithm takes a long time. The retrieval results will be better when the system retrieves the data with synonyms of words in retrieval expression, the integration of character base and word base retrieval, and with the user""s profile, but the retrieval time will be long.
As mentioned-above, when using the elaborate retrieval algorithm, the retrieval processing takes a long time. However, if the retrieval results formerly obtained is provided, the retrieval results are poor to the user.
It is an object of the present invention to provide an information retrieval apparatus and a method to present at least one retrieval result of high quality to the user quickly.
According to the present invention, there is provided an information retrieval apparatus, comprising: a receiving means for receiving a retrieval request from a user; a first retrieval means for retrieving information from a database in response to the retrieval request; a retrieval result memory means for storing the information retrieved by said first retrieval means; and a second retrieval means for retrieving detailed or additional information from the database by using the retrieval request in case a new retrieval request is not received by said receiving means.
Further in accordance with the present invention, there is also provided a method for retrieving information from a database; comprising the steps of: receiving a retrieval request from a user; retrieving the information from the database in response to the retrieval request; storing the information retrieved at the retrieving step in a retrieval result memory; and advanced retrieving information from the database by using the retrieval request in case new retrieval request is not received at the receiving step.
Further in accordance with the present invention, there is also provided a computer readable memory containing computer readable instructions to retrieve information from a database, comprising: an instruction means for causing a computer to receive a retrieval request from a user; an instruction means for causing a computer to retrieve the information from the database in response to the retrieval request; an instruction means for causing a computer to store the retrieved information in a retrieval result memory; and an instruction means for causing a computer to retrieve detail information from the database by using the retrieval request in case new retrieval request is not received.